Enable polymorphic inlining of StringBase [] and StringBase codeUnitAt

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 17272be4aa22e33d93c45e30c40114d79efecec4..7d9613989d9b0ec7a7f83aca90de92020b86abfd 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -183,6 +183,8 @@ class Range;
 
 // A list of core functions that internally dispatch based on received id.
 #define POLYMORPHIC_TARGET_LIST(V)                                             \
+  V(_StringBase, [], StringBaseCharAt, 585372763)                              \
+  V(_StringBase, codeUnitAt, StringBaseCodeUnitAt, 1958436584)                 \
   V(_TypedList, _getInt8, ByteArrayBaseGetInt8, 272598802)                     \
   V(_TypedList, _getUint8, ByteArrayBaseGetUint8, 831354841)                   \
   V(_TypedList, _getInt16, ByteArrayBaseGetInt16, 1832126257)                  \
@@ -3698,9 +3700,7 @@ class StringFromCharCodeInstr : public TemplateDefinition<1> {
  public:
   StringFromCharCodeInstr(Value* char_code, intptr_t cid) : cid_(cid) {
     ASSERT(char_code != NULL);
-    ASSERT(char_code->definition()->IsLoadIndexed() &&
-           (char_code->definition()->AsLoadIndexed()->class_id() ==
-            kOneByteStringCid));
+    ASSERT(char_code->definition()->IsLoadIndexed());
     SetInputAt(0, char_code);
   }